The present invention relates to a process for the enhanced recovery of oil from an underground oil-containing formation, more particularly to a process for displacing oil by injecting into and driving through such a formation a mixture containing carbon dioxide (CO.sub.2), a surfactant and water, and most particularly to an improved CO.sub.2 drive process which utilizes an alcohol ethoxycarboxylate surfactant.
It is known in the art that oil can be displaced within and recovered from a subterranean reservoir by injecting a drive fluid containing pressurized (substantially liquid) CO.sub.2, water and a surfactant. Examples of such drive processes are to be found in the disclosures of U.S. Pat. No. 3,342,256, entitled Method for Recovering Oil from Subterranean Formations, which issued to G. G. Bernard et al on Sept. 19, 1967, U.S. Pat. No. 4,380,266, entitled Reservoir-tailored CO.sub.2 -aided Oil Recovery Process, which issued to S. L. Wellington on Apr. 19, 1983 and of U.S. Pat. No. 4,502,538, entitled Polyalkoxy Sulfonate, CO.sub.2 and Brine Drive Process for Oil Recovery, which issued to Wellington et al on Mar. 5, 1985.
Of particular interest to the present invention is the surfactant utilized in such a CO.sub.2 drive process. Use is made of the surfactant to form a "foam" which reduces the mobility of the CO.sub.2 in the reservoir. It is well recognized in the art that many reservoir flood or drive processes, including those utilizing CO.sub.2, suffer from a tendency of the injected fluids to sweep oil from only a limited volume of the reservoir. The fluids breakthrough to the recovery well before they have the opportunity to efficiently invade and displace oil from the reservoir rock. The above-cited patents, as well as in the other art described therein, recite the benefits of several different surfactant compounds for mobility control in CO.sub.2 drive processes. Specific mention is made of polyalkoxylated alcohols and phenols, polyalkoxylated alcohol sulfates, alkyl sulfoacetates, block polymers of polyoxyethylene and polyoxypropylene, petroleum sulfonates, aliphatic alcohols, naphthenyl alcohol, amorphous glycosides, and polyalkoxylated alcohol and phenol sulfonates, and polyalkoxylated alcohol and phenol glyceryl sulfonates. At least one alcohol ethoxysulfate surfactant has been used in CO.sub.2 drive processes in the oilfield (L. Holm, J. Petroleum Technol., 22, 1409-1506 (1970); L. Holm "CO.sub.2 Diversion Using Foam in an Immiscible CO.sub.2 Field Project," Paper No. SPE/DOE 14963 presented at the SPE/DOE Fifth Joint Symposium on Enhanced Oil Recovery, Tulsa, OK, Apr. 20-23, 1986; and J. R Heller et al, SPE Paper No. 14395, presented at the Sixtieth Annual Conference and Exhibition of the Society of Petroleum Engineers of AIME, Las Vegas, Nev., Sept. 22-25, 1985).